1. Field of the Invention
The present invention generally relates to a wobble-signal detecting device for detecting a wobble signal from a recording medium having a recordable information recording track which, or recordable information recording tracks, each of which wobbles at a predetermined frequency (this means that a track formed on the disc wobbles in such a manner that, when the rotation of the disc is ideally controlled, the wobbles occur for a pickup at the predetermined frequency, here and hereinafter) and pre-pits formed at predetermined intervals in areas between the information recording tracks, and, to an information recording apparatus such as a DVD-R drive, a recordable-optical-disc recording and reproducing apparatus or the like using the above-mentioned wobble-signal detecting device.
2. Description of the Related Art
In the related art, there is an optical recording medium having a wobbling groove and pits formed in areas between the grooves at predetermined intervals and a recording and reproducing apparatus for the optical recording medium (for example, see Japanese Laid-Open Patent Application No. 9-326138). In such an apparatus, it is possible to obtain address information and disc rotation control information precisely even with a narrow track pitch, and high-density recording is enabled.
Further, there is a recording-clock-signal generating device for a recording apparatus which records data based on a recording clock signal phase-locked to a wobble signal on an optical disc having a data recording track which wobbles in accordance with a wobble signal having a predetermined frequency component and pre-pits having a predetermined phase relationship with the wobble signal (for example, see Japanese Laid-Open Patent Application No. 10-293926).
In such an apparatus, the phase of the recording clock signal is adjusted using a phase adjusting signal generated as a result of the phase of the extracted wobble signal and the phase of the pre-pit detection signal being compared with one another, and it is possible to generate the recording clock signal precisely in synchronization with the disc rotation even when influence of cross talk due to the wobble signal of an adjacent groove track exists.
On a recordable optical disc, address information and a synchronization signal for rotation control and recording position control are previously recorded as a pre-format.
As one of the methods for recording such preformat information, there is a method in which, for example, a so-called CD-R has a groove (data recording track) wobbling at a predetermined frequency and address information is recorded as a result of the wobbles being frequency-modulated.
In order to extract the wobble signal, a socalled push-pull signal is caused to pass through a band pass filter (referred to as simply xe2x80x98BPSxe2x80x99, hereinafter), the central frequency of which is the above-mentioned predetermined frequency, and rotation control is performed so that the frequency of the thus-extracted wobble signal becomes the predetermined frequency.
As is well known, the push-pull signal is the difference (differential signal) between the outputs of two divisions of a light-receiving device, which two divisions are obtained as a result of the light-receiving device being divided by a line parallel to the direction of the tangent of the track at a target position, and receiving the light reflected by the disc.
Further, the wobble signal is used as a reference signal for generating the recording clock signal, and, thereby, it is possible to record data in synchronization with the rotation of the disc.
Japanese Laid-Open Patent Application No. 9-326138 proposes an optical disc having a wobbling groove and pits formed in areas (lands) between the grooves at predetermined intervals, and it is possible to precisely obtain address information and disc rotation control information even with a narrow track pitch.
This method is different from another method in which address information is arranged at the start of a sector. That is, in this method, no address pits exist in the groove which is the data recording track. As a result, high-density recording is enabled, recorded information is not divided by the address information, and superior interchangeability with a reproduction-only disc is provided.
Such an apparatus uses a method in which the wobble signal and pit signal are read out simultaneously using one beam spot using the push-pull method, and, similar to the case of CD-R, the wobble signal is extracted through BPF, is used for disc rotation control, and, also, is used as a reference signal for generating the recording clock signal. A DVD-R studied recently has a form similar to the above-described optical disc.
For example, for DVD-R, the track pitch is narrowed for performing high-density recording. Thereby, so-called cross talk from a groove adjacent to a groove on which an optical beam is incident cannot be ignored.
When cross talk from adjacent inner and outer grooves exists, the wobble signal is interfered with by wobble components of the adjacent grooves, and, as a result, fluctuates in the amplitude and/or phase thereof. In particular, when phase fluctuation occurs, it is not possible to generate the recording clock signal precisely in synchronization with rotation of the disc.
In order to solve this problem, a device such as that disclosed in Japanese Laid-Open Patent Application No. 10-293926 is proposed.
This is a recording-clock-signal generating device for a recording apparatus which records data based on the recording clock signal which is phase-locked to the wobble signal on an optical disc having the data recording track which wobbles in accordance with the wobble signal having the predetermined frequency component and pre-pits having the predetermined phase relationship with the wobble signal. In this device, the phase of the recording clock signal is adjusted using the phase adjusting signal generated as a result of the phase of the extracted wobble signal and the phase of the pre-pit detection signal being compared with one another.
Thereby, it is possible to generate the recording clock signal precisely in synchronization with the disc rotation even when influence of cross talk due to the wobble signal of an adjacent groove track exists.
Thus, the wobble signal is important for disc rotation control and generation of the recording clock signal, and, in particular, detection of the wobble signal having few jitters (phase fluctuation) is indispensable for providing with high accuracy the recording clock signal in synchronization with disc rotation.
However, there is a cause for fluctuations in the amplitude and/or phase of the wobble signal other than the influence of cross talk due to the wobble signal of an adjacent groove track.
That is, the push-pull signal detected by the push-pull method from a recording medium having a wobbling groove and pits formed in lands at predetermined intervals includes the wobble component and pre-pit components, as shown in FIG. 1A. Then, when the wobble signal is extracted from this push-pull signal through a BPF, the central frequency of which is the wobble frequency, the signal including not only the wobble component but also the wobble-frequency component of the pre-pit components is extracted. This wobble-frequency component of the pre-pit components becomes the cause for fluctuations in the amplitude and/or phase of the wobble signal.
Normally, as shown in FIG. 1A, the pre-pit-signal components are larger than the wobble component, so the wobble-frequency component of the pre-pit components becomes larger as the amplitude of the pre-pit components becomes larger, and, thereby, the influence thereof to the wobble signal (wobble component+wobble-frequency component of the pre-pit components) cannot be ignored.
For example, for the DVD-R, pre-pits are formed in a land adjacent to and the outer side of a groove, and, in a land adjacent to and on the inner side, pre-pits for the immediately inner groove are formed.
The outer-side pre-pits, that is, the pre-pits for the target groove are formed in a fixed phase relationship with the wobbles of the target groove. However, because the inner-side pre-pits are pre-pits for the next inner groove, the phase relationship with the wobbles of the target groove varies depending on position.
The pre-pit components from both the outer-side and inner-side pre-pits are included in the push-pull signal for the target track.
In FIG. 1A, the upper pre-pit components 4 correspond to the outer-side pre-pits and the lower pre-pit components correspond to the inner-side pre-pits.
Further, because the pre-pits indicate address information and so forth by presence/absence thereof, the pre-pits are not formed in a fixed pattern, and, thereby, not only each frequency component but also the wobble-frequency component of the pre-pit signal vary locally.
Therefore, the degree in which the pre-pit components corresponding to the inner-side and outer-side pre-pits vary the amplitude and/or phase of the wobble signal varies depending on the pattern of the pre-pits.
The amplitude/phase fluctuation of the wobble signal due to the pre-pits is different from phase fluctuation due to cross talk in a relatively low frequency compared to phase fluctuation in a relatively high frequency.
Accordingly, to the wobble component of a fixed frequency, the wobble-frequency component of the pre-pit components of the same frequency, the phase of which varies every moment and also the amplitude of which varies, is added. As a result, the amplitude and phase or the wobble signal vary in every moment from the original amplitude and phase, and, thereby, the jitters of the recording clock signal generated from the wobble signal increase.
Further, depending on the relationship between the amplitude of the wobble component and the amplitude of the pre-pit components, the amplitude of the wobble signal may vary as if the wobble signal disappears, as shown in FIG. 1B. Thereby, disc rotation control and, in particular, generation of the recording clock signal are greatly adversely affected.
The present invention has been devised in consideration of the above points, and, an object of the present invention is to provide a wobble-signal detecting device which detects a wobble signal, from a recording medium having a groove which, or grooves each of which wobbles at a predetermined frequency and pre-pits formed in lands at predetermined intervals, having a lesser phase fluctuation by reducing amplitude and phase fluctuation of the wobble signal due to the pre-pits, and to provide an information recording apparatus which can record data on a disc in synchronization with the rotation of the disc with high accuracy.
A wobble-signal detecting device, according to the present invention, for detecting a wobble signal based on a signal which is the difference between outputs of two divisions of a light receiving device, the two divisions being located on both sides of a line parallel to an information recording track at a target position thereof, the light receiving device receiving light reflected by a recording medium as a result of an optical beam being incident on the recording medium, the recording medium having the information recording track which or the information recording tracks each of which wobbles at a predetermined frequency, and pre-pits formed at predetermined intervals in areas between the information recording tracks, comprises:
a pre-pit controlling portion which removes or reduces the pre-pit components of the signal which is the difference between the outputs of the two divisions of the light receiving device, and outputs a pre-pit-component-controlled signal: and
a wobble-frequency-component extracting portion which extracts wobble-frequency components from the pre-pit-component-controlled signal and outputs a wobble-frequency-component signal, the wobble signal being obtained based on the wobble-frequency-component signal.
In this arrangement, the pre-pit components included in the push-pull signal (signal which is the difference between outputs of two divisions of a light receiving device) is removed or reduced. Thereby, it is possible to reduce the influence of the pre-pit components to the wobble signal, to reduce amplitude and phase fluctuation of the wobble-frequency-component signal due to the pre-pit components, and to reduce phase fluctuation of the wobble signal (two-value signal).
A wobble-signal detecting device, according to another aspect of the present invention, for detecting a wobble signal based on a signal which is the difference between outputs of two divisions of a light receiving device, the two divisions being located on both sides of a line parallel to an information recording track at a target position thereof, the light receiving device receiving light reflected by a recording medium as a result of an optical beam being incident on the recording medium, the recording medium having the information recording track which or the information recording tracks each of which wobbles at a predetermined frequency, and pre-pits formed at predetermined intervals in areas between the information recording tracks, comprises:
a limiter which limits the amplitude of the signal which is the difference between the outputs of the two divisions of the light receiving device and outputs an amplitude-limited signal so that the amplitude of the amplitude-limited signal does not exceed both or at least either one of a predetermined upper-limit value and a predetermined lower-limit value; and
a wobble-frequency-component extracting portion which extracts wobble-frequency components from the amplitude-limited signal and outputs a wobble-frequency-component signal, the wobble signal being obtained based on the wobble-frequency-component signal.
In this arrangement, the amplitudes of the pre-pit components included in the push-pull signal (signal which is the difference between outputs of two divisions of a light receiving device) are limited. Thereby, it is possible to reduce the influence of the pre-pit components on the wobble signal, to reduce amplitude and phase fluctuation of the wobble-frequency-component signal due to the pre-pit components, and to reduce phase fluctuation of the wobble signal (two-value signal).
The upper-limit value and lower-limit value used by the limiter may be variable. Thereby, it is possible to set the upper-limit value and lower-limit value arbitrarily. Accordingly, it is possible to effectively cope with a case where the optimum values of the upper-limit value and lower-limit value are different depending on the type of the disc, whether data is being recorded or being reproduced, and so forth.
The wobble-signal detecting device may further comprise:
a filter which cuts off high-frequency components of the output signal of the limiter or the signal which is the difference between the outputs of the two divisions of the light receiving device;
an adder which adds a predetermined value to the output of the filter; and
a subtractor which subtracts a predetermined value from the output of the filter,
wherein the limiter uses the output of the adder as the upper-limit value and uses the output of the subtractor as the lower-limit value.
In this arrangement, the upper-limit value and lower-limit value used by the limiter for limiting the amplitude of the push-pull signal change in accordance with the change in the push-pull signal. As a result, it is possible to limit the amplitudes of the pre-pit components more precisely. In particular, it is possible to effectively limit the amplitudes of the pre-pit components not located at the peaks of the wobbles. Accordingly, it is possible to further reduce the influence of the pre-pit components to the wobble signal, to further reduce amplitude and phase fluctuation of the wobble-frequency-component signal due to the pre-pit components, and to further reduce phase fluctuation of the wobble signal (two-value signal).
The predetermined values used by the adder and subtractor may be variable. As a result, it is possible to set these predetermined values arbitrarily. Thereby, it is possible to set the upper-limit value and lower-limit value arbitrarily. Accordingly, it is possible to effectively cope with a case where the optimum values of the upper-limit value and lower-limit value are different depending on the type of the disc, whether data is being recorded or being reproduced, and so forth.
A wobble-signal detecting device, according to another aspect of the present invention, for detecting a wobble signal based on a signal which is the difference between outputs of two divisions of a light receiving device, the two divisions being located on both sides of a line parallel to an information recording track at a target position thereof, the light receiving device receiving light reflected by a recording medium as a result of an optical beam being incident on the recording medium, the recording medium having the information recording track which or the information recording tracks each of which wobbles at a predetermined frequency, and pre-pits formed at predetermined intervals in areas between the information recording tracks, comprises:
a first pre-pit detecting portion which detects the pre-pits formed in an area on one side of the information recording track;
a second pre-pit detecting portion which detects the pre-pits formed in an area on the other side of the information recording track;
a timing-signal generating portion which generates a sample/hold timing signal based on the outputs of the first pre-pit detecting portion and the second pre-pit detecting portion;
a sample/hold portion which samples/holds the signal which is the difference between the outputs of the two divisions of the light receiving device based on the sample/hold timing signal; and
a wobble-frequency-component extracting portion which extracts wobble-frequency components from the output signal of the sample/hold portion and outputs a wobble-frequency-component signal, the wobble signal being obtained based on the wobble-frequency-component signal.
In this arrangement, the push-pull signal is held during periods during which the pre-pits occur and is sampled during all the other periods. Thereby, a signal from which the pre-pit components are removed is obtained. As a result, it is possible to reduce the pre-pit components so much that the pre-pit components can be approximately neglected with respect to the wobble component. Accordingly, it is possible to reduce the influence of the pre-pit components on the wobble signal, to reduce amplitude and phase fluctuation of the wobble signal due to the pre-pit components, and to reduce phase fluctuation of the wobble signal (two-value signal).
The timing-signal generating portion may comprise:
a first pre-pit synchronized-signal generating portion which generates a first pre-pit synchronized signal phase-locked to the output of the first pre-pit detecting portion; and
a second pre-pit synchronized-signal generating portion which generates a second pre-pit synchronized signal phase-locked to the output of the second pre-pit detecting portion;
and a portion which generates, from the first pre-pit synchronized signal and the second pre-pit synchronized signal, the sample/hold timing signal for holding the signal which is the difference between the outputs of the two divisions of the light receiving device only during periods during which the first and second pre-pits may occur.
In this arrangement, the sample/hold-timing signal is generated to be phase-locked to the occurrences of the pre-pits using a PLL circuit or the like. Accordingly, it is possible to remove the pre-pit components precisely through a simple arrangement. Thus, it is possible to effectively reduce phase fluctuation of the wobble signal (two-value signal) due to the pre-pit components.
Further in this arrangement, it is possible to easily predict the times at which the pre-pits occur. As a result, it is possible to prevent the push-pull signal from being held during the time periods during which it is not necessary to hold the push-pull signal. Thus, it is possible to more effectively reduce and phase fluctuation of the wobble signal (two-value signal) due to the pre-pit components.
An information recording apparatus, according to the present invention, for recording information on a recording medium having an information recording track which or the information recording tracks each of which wobbles at a predetermined frequency, and pre-pits formed at predetermined intervals in areas between the information recording tracks, the apparatus comprising:
a wobble-signal detecting device, which is any one of the above-described wobble-signal detecting devices, for detecting a wobble signal based on a signal which is the difference between outputs of two divisions of light receiving device, the two divisions being located on both sides of a line parallel to an information recording track at a target position thereof, the light receiving device receiving light reflected by the recording medium as a result of an optical beam being incident on the recording medium;
a rotation controlling portion which controls the rotation of the recording medium so that the frequency of the wobble signal becomes a predetermined frequency;
a recording-clock-signal generating portion which generates a recording clock signal from the wobble signal; and
a recording portion which records information on the recording medium using the recording clock signal as a reference signal.
In this arrangement, the wobble signal (two-value signal), phase fluctuation of which due to the pre-pit components is reduced, is provided by the wobble-signal detecting device, and is used for rotation control and generation of the recording clock signal. Thereby, the recording clock signal which is synchronized with the rotation of the disc with high accuracy and has few jitters can be obtained, and, as a result, it is possible to record information with high accuracy.
Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.